Simplify the following expression: $n = \dfrac{5}{7p} + \dfrac{1}{9p}$
Solution: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $7p$ and $9p$ $\lcm(7p, 9p) = 63p$ $ n = \dfrac{9}{9} \cdot \dfrac{5}{7p} + \dfrac{7}{7} \cdot \dfrac{1}{9p} $ $n = \dfrac{45}{63p} + \dfrac{7}{63p}$ $n = \dfrac{45 +7}{63p}$ $n = \dfrac{52}{63p}$